This application is focused on the isolation of novel genes or functions critical to the differentiated phenotype of the pulmonary alveolar type 2 epithelial cell. The differentiated function of these cells is crucial to alveolar restructuring associated with lung growth, lung repair following injury, and maintaining an air-filled alveolus by surfactant for normal gas exchange. In addition to its critical role in surfactant biology, the type 2 cell is a progenitor cell for the alveolus having the ability to divide and terminally differentiate into type 1 cells. There are major gaps in our understanding of repair of the alveolar epithelium, and other features associated with proposed, but poorly characterized, type 2 cell functions such as immune defense, electrolyte transport, and remodeling of extracellular matrix. Through the differential screening of a type 2 cell cDNA library made from type 2 cells obtained from adult rat lung, we have isolated genes expressed in the type 2 cell which, by partial sequence analysis and northern analysis, have not been previously described, and are preferentially expressed in type 2 cells. We differentially screened a type 2 cell cDNA library against kidney and intestinal epithelial cells, which represents a comparison between type 2 cells and antigenically related epithelial cells. In support of these genes having differentiation-related functions, we have shown that one of these genes is preferentially expressed in differentiated type 2 cells, but not dedifferentiated type 2 cells. In addition, we isolated another gene which is expressed only in lung. Our inability to detect significant DNA sequence similarities with known lung genes after partial sequencing further supports that they are not previously described genes expressed in type 2 cells. We propose to further characterize these genes by DNA sequence analysis, to determine their distribution in adult and developing lung by in situ hybridization, and to define their expression in relation to differentiation in order to use these genes as markers of differentiation, and to study factors which regulate their expression using several new culture systems. The products of this research will be new information about specialized functions of the type 2 cell, and new insights into the control of type 2 cell differentiation. This work represents basic research of the alveolar epithelium, and there are no immediate clinical applications. However, there are numerous long term clinical benefits from understanding the biology of the alveolar epithelium such as the consequences of acute alveolar injury on alveolar restructuring.